There are many applications where a nanotube, e.g., a carbon nanotube (CNT), or an array of nanotubes, can be employed as a sensing or active device element in an electrical probe or electronic device. In these applications, electrical contact must be made with the nanotube, which requires accurate positioning of the nanotube with respect to various conductive links (i.e. interconnects) and other circuitry.
Aside from the need for precise alignment, properties of the nanotube also need to be controlled in order to provide device performance according to desired specifications. For example, many transistor applications for CNTs are best achieved with single wall carbon nanotubes (SWNT) rather than multi-wall carbon nanotubes (MWNT). Furthermore, as an active element of a transistor, a semiconducting SWNT, rather than a metallic SWNT, is required. For other applications such as interconnects and nanoprobes, however, a metallic CNT is preferred.
Existing fabrication methods for CNT devices do not fully address both needs for alignment and property control. In addition, in CNT electrical device fabrication, at least one interconnect level may be processed before CNT deposition. The most common metallization schemes, e.g., with aluminum and copper interconnects, often impose thermal budget constraints for subsequent processing steps. Chemical vapor deposition (CVD) methods, which are typically used for depositing CNTs, are not compatible with aluminum or copper interconnects because of the relatively high temperatures involved.